US President Barack Obama has arrived in Tokyo on the first leg of a 4-nation diplomatic tour of Asia.

The president was welcomed at Haneda Airport by US Ambassador to Japan Caroline Kennedy and Japan's Ambassador to the United States Kenichiro Sasae.

Obama's first meeting with Japanese Prime Minister Shinzo Abe took place in an informal and intimate atmosphere at an upscale sushi restaurant in Tokyo's Ginza district.

Obama greeted the prime minister by his first name, to which Abe replied "how are you?" in English.

The US president is set to attend on Thursday a welcome ceremony at the Imperial Palace, before the formal summit meeting with Abe.